As is well known, phase aberration corrections (PAC) are applied in ultrasound imaging systems to correct phase errors in ultrasound beams which are caused by nearfield inhomogeneities in tissue density and/or in acoustic velocity. Ultrasound imaging applications in which such phase errors are most degrading include abdominal imaging of difficult patients, transcranial imaging, and breast imaging. Further, as is well known, the effects of such phase errors are more prominent when utilizing large aperture transducer arrays, high frequency imaging, and high precision beamforming with a large number of channels.
An assumption which is used by most commercial ultrasound scanners for all focusing and angle steering calculations is that the propagation velocity of ultrasound waves in human tissue is a constant (typically a value of 1540 m/s is used). Unfortunately, this assumption is not valid. In reality, a human body is comprised of inhomogeneous layers of different tissues, for example, fat, muscle, bone, and, so forth, with these layers having bumps and ridges of varying thicknesses, densities, and acoustic velocities. As a result, the propagation velocity of ultrasound waves in the human body varies from approximately 1470 m/s in fat, to greater than 1600 m/s in muscle and nervous tissue, to as much as 3700 m/s in bone. Using the assumption that the human body is comprised of a uniform tissue medium of constant propagation velocity, the presence of inhomogeneous tissue layers results in image artifacts, range shifts, geometric distortions, broadening of transducer beam patterns which degrade ideal diffraction limited lateral resolution, and increased side lobes which reduce contrast resolution in an image. Most approaches used to make phase aberration correction, utilize dedicated hardware which results in an expensive solution.
In light of the above, there is a need in the art for apparatus for performing adaptive phase aberration correction which is less expensive than prior apparatus.